“Mother, have you heard about our summer holidays yet?” asked Julian, at the breakfast-table. “Can we go to Polzeath as usual?”

“I’m afraid not,” says his mother. “They are quite full up this year.”

So begins Enid Blyton’s first Famous Five adventure, Five on a Treasure Island, which was published 75 years ago this September and set in Blyton’s adopted home, Dorset’s Isle of Purbeck.

With Cornwall off the cards, Julian, Dick and Anne’s parents pack them off to Aunt Fanny, Uncle Quentin and their “lonely” cousin Georgina, in Kirrin Bay.

Purbeck’s not really an isle, more a peninsula, surrounded by water on three sides, with the island-dotted Poole Harbour to the north, the seaside town of Swanage (where Blyton used to stay in the The Grand Hotel in the 1950s) to the east, and the secluded coves and bays of Dorset’s Jurassic Coast to the south.

Born on August 11, 1897 (she would be 120 this year), Blyton’s main home from the late 1930s was Green Hedges (named by her readers in a competition) in Beaconsfield, a London commuter town bordering the Chiltern Hills, but she had a love affair with Purbeck. She spent three holidays there every year for more than two decades, even buying the Isle of Purbeck Golf Club with her husband Kenneth in 1950.

With its green hills rolling like sleeping dragons, dramatic cliffs plunging down into the sea, and the ruins of Corfe Castle at its heart, it’s easy to see why she kept coming back and mined the area for her famous children’s books.

We take a picturesque ride in the Pullman Observation Car, right behind the engine on the impeccably well-kept Swanage Railway steam train from Swanage to Corfe Castle.

Blyton did just that in 1941, arriving at what she turned into Kirrin Castle, on Kirrin Island, owned by George’s family, where the cousins and Timmy the dog discover gold in the dungeon in Five on a Treasure Island.

There may not be any gold bullion for us to find, but our three-year-old son Ollie enjoys hunting for the six shields that are hidden around the 11th-century ruins, and answering questions from the facts written on each that will reward him with a rubber Corfe Castle wristband.

A short drive from the castle is Blue Pool, a former clay pit that’s naturally filled with rainwater, surrounded with scented pines and rhododendrons, and perhaps the most beautifully calm spot in the whole of Purbeck.

Blyton was a fan and described it in 1946’s Five Go Off in a Caravan, where they picnic beside an “enormous blue lake that glittered in the August sunshine”.

We wander around the 8ha site, sipping ginger beer and watching the colour of the lake change subtly from blue to green.

Home for our stay is Moonfleet Manor, just to the west of Weymouth, a Georgian country pile that overlooks the iconic pebbles of Chesil Beach.

Part of the Luxury Family Hotel Group, it has its own literary connection, having inspired J Meade Falkner’s 1898 tale of smuggling and shipwrecks, Moonfleet.

The hotel has its own Timmy, a tea-coloured spaniel called Snoopy, who befriends all the littler guests, and Blyton would have approved of the exotic antique decor, with menus from old cruise ships and tiger skins adorning the walls. In the hall is a chest full of buckets and spades and a rack of welly boots.

There are three swimming pools, an enormous indoor play area and a fairy door hunt to keep little ones entertained when they’re not exploring Dorset.

The isle of Purbeck.

It’s just an hour’s drive through Purbeck to Poole, from where we catch the ferry to the mysterious Brownsea Island, Blyton’s Whispering Island – and also described as Keep Away Island in Five Have a Mystery to Solve.

In her day, it was owned by Mary Bonham-Christie, a recluse who let it return to nature and would not tolerate visitors.

Today it’s owned by Britain’s National Trust, who cleared the island of its rampant rhododendrons. As it’s a perfect summer’s day, we take a picnic of goat’s cheese and roasted red pepper sandwiches, juicy oranges and homemade chocolate chip biscuits down the steps to South Shore’s sandy beach, overlooking the smaller Furzey island, where Ollie paddles and throws handfuls of seaweed into the water.

Moonfleet Manor. Photo: Alex Brown/flickr

Rejuvenated, we go in search of Brownsea’s most famous residents: red squirrels.

Besides the wetland and lagoon to the north, managed by the Dorset Wildlife Trust, much of the island is woodland, but no matter how much we wander around looking up into the trees, we can’t see a single squirrel.

Then, just as we near the church, a flash of red darts across the path in front of us, followed by a peacock. We stop, crouch, and are joined by Hayley, a wildlife photographer with a tub of unshelled pistachios.

Soon our little squirrel is back and happily cracking into the nuts, as we watch, spellbound by its little paws and tufty red ears, like something out of a children’s book.

On the drive back to our hotel, I verbally recount the whole of Five on a Treasure Island, with its shipwreck, gold and dastardly villains, to an unusually rapt Ollie, a sure sign that Blyton’s power of storytelling has not waned in 75 years. And after the few days we’ve had here, neither has the lure of her beloved Purbeck.

Staying there: Moonfleet Manor has family rooms from STG210 ($A350) B&B for two adults and two children, and from STG120 ($A200) B&B for a standard double room. Children up to 15 stay free when staying in the parents’ room. Details: moonfleetmanorhotel.co.uk

Playing there: Return ticket from Swanage to Corfe Castle: STG12.50 ($A20.83) adults, STG7.60 ($A12.66) children (under 5s, free). Details: swanagerailway.co.uk

Corfe Castle entrance prices: from STG9 ($A15) adults, STG4.50 ($A7.50) children. Details: nationaltrust.org.uk/corfe-castle

Brownsea Island entrance prices: from STG6.75 ($A11.25) adults, STG3.35 ($A5.58) children. Details: nationaltrust.org.uk/brownsea-island

-PA